Edit by Ausir
I was asked by Jessica Urquhart to take the link down, as this (European) version of the demo was not supposed to be released until September. The US version will be released exclusively at GameSpy soon.

More Edit
The demo has been released officially at GameSpy (subscriber only, of course), but even though it was deleted by CD Projekt, the leaked version is all around the net now (like here. By the way, the supposedly different US and UK version have the same filesize... Maybe they have armour/armor spelt differently? If that's the case, better don't touch the leaked version!

Yet another update
It turns out CD Projekt *did* have a written permission from Interplay to release the demo, but there was an internal discommunication between the ones at IPLY who gave the demo to CDP and the ones who gave it exclusively to GameSpy. You can now download it from CD Projekt again, anyway.